Elad1002,
Some gentle exercises/activities you can do are:
Stairs, avoid over doing.
Terminal knee extension, lying on your back, with a towel roll under your knee, gently lift your lower leg, no weights.
The Chair Pew exercise, start with less time than mentioned, you can get sore very fast if you over do this activity,
Your challenge is to avoid over doing any of these exercises/activities, listen to your knee and if it says stop, stop!